What am I missing here. Although my background is in electronics and
electrical engineering, I've specialized in power rather than communications
for thirty years. My scant and no doubt obsolete communications theory
always held that for great short-wave reception, double or even triple
conversion receivers were the norm. Now I see advertised, SW radios with
"... highly sensitive and selective latest state of the art single
conversion analog tuner circuitry....". What breakthrough has made single
conversion so state of the art?

Maybe read what Elecraft sez -- URL:

http://www.elecraft.com/Apps/why_is_...ver_single.htm
--
CL -- I doubt, therefore I might be !






"Larry" wrote in message
...
What am I missing here. Although my background is in electronics and
electrical engineering, I've specialized in power rather than
communications for thirty years. My scant and no doubt obsolete
communications theory always held that for great short-wave reception,
double or even triple conversion receivers were the norm. Now I see
advertised, SW radios with "... highly sensitive and selective latest
state of the art single conversion analog tuner circuitry....". What
breakthrough has made single conversion so state of the art?

"Larry" ) writes:
What am I missing here. Although my background is in electronics and
electrical engineering, I've specialized in power rather than communications
for thirty years. My scant and no doubt obsolete communications theory
always held that for great short-wave reception, double or even triple
conversion receivers were the norm. Now I see advertised, SW radios with
"... highly sensitive and selective latest state of the art single
conversion analog tuner circuitry....". What breakthrough has made single
conversion so state of the art?


The number of conversions in a receiver means nothing. It's the detail
behind it that counts.

When Howard Armstrong came up with the superheterodyne receiver during or
right after WWI, tubes were pretty non-existent in terms of specs. You needed
to convert radio to a lower frequency to get any sort of amplification. So
all superhets in the early days went to a lower frequency.

But then they realized a problem with that. Every time two frequencies
are heterodyned together, the sum and the difference result. This means
that there is an image frequency, ie one that is incidental to the
heterodyning but which you you don't want. If your IF frequency is
455KHz, and you want to receive WWV at 10MHz, there will also be an
image twice the IF frequency away (higher or lower depending on
whether the receiver's local oscillator is higher or lower than the
signal frequency).

To get rid of that image frequency, you need the front end to be
selective enough to knock it out. At low frequencies, like the AM
broadcast band, it's easy, because the image is distant from the
desired signal by a fair amount. But as you move into the shortwave
frequencies, that 455KHz becomes a smaller and smaller percentage of the
signal frequency, and it becomes harder to get rid of the image. There
were all kinds of cheap receivers in the past (and maybe even today) that
had 455KHz IFs and you'd see reviews and they'd say "basically there is
no image rejection on the 20 to 30MHz band. The only way to stay with
455KHz and get good image rejection is to add more tuned circuits at
the front end, which some receivers like the HRO, did.

You can raise the IF frequency to improve image rejection. If you've
got a 9MHz IF, then you can get by with fairly little front end selectivity,
because the image is 18MHz away from the signal you want to tune. It's
easy to reject a signal that far off.

But for quite some time, this wasn't possible because nobody could make
filters that high up. So the double-conversion receiver came into use.
Convert the signal down to a not too low frequency, to improve image
rejection, but then convert down to the usual 455KHz after that to get
good selectivity. If you have enough selectivity at the first IF so
it can reject a signal 910KHz away (and this is relatively easy for a fixed
IF where you don't have to tune a bunch of tuned circuits at the same
time across the band), then you've mostly solved the image rejection problem.

The double conversion in this case is just a workaround, to get good
image rejection, but also good selectivity with the second IF frequency.

When double conversion first hit, they'd often do a mix, where the
receiver would be single conversion to 455KHz on the lower bands, and
then a stage of selectivity at 2 or 3MHz would kick in on the higher
band(s) where it was needed, before another conversion to 455KHz.
These still used a tuneable local oscillator on the first mixer.

Of course, one whole layout of double conversion was to make the
first local oscillator crystal controlled. Then you'd have what
amounted to a tuneable receiver with a 455KHz IF, that tuned a fixed
range, often 500KHz. It would tune something like 3 to 3.5MHz, and
the first conversion would convert the desired signals to that range.
One disadvantage of this is that you needed a crystal for every 500KHz
or whatever the tuneable portion tuned. (Sometimes it got far worse,
with the receiver tuning 200KHz at a time.) On the other hand, the
advantage of this scheme was that by having the receiver tune a small
segment of the spectrum, and only tune that 3 to 3.5MHz band, you could
afford to make it linear tuning, and could afford to calibrate it well.
So these receivers brought in a level of tuning accuracy that often
hadn't been seen before.

There is another problem with conversion besides images. Every conversion
decreases the immunity to overload, adds complication, and adds another
oscillator that if not carefully shielded and layed out, will cause
spurious responses.

So starting in the late fifties and early sixties, a new wave of
single conversion receivers hit. Crystal filters came along, that
offered good selectivity in the HF range, 9MHz being a common frequency.
That gave good selectivity and allowed for good image rejection with
only one IF frequency. Instead of having the ultimate selectivity way
down the signal chain, you could place it right after the first mixer,
leaving a stage or two before that good crystal filter. (Since the stages
after the crystal filter only had to see what was within the bandwidth
of that filter, it took a really strong signal to overload anything after
that filter, while in some of the previous examples many stages would
be seeing a lot of signal.)

Of course there were problems with that scheme. If the IF is in the
spectrum you want to receive, it can't be used around that frequency.
So there'd be a small gap around the IF frequency that you couldn't
really use the receiver. Also, crystal filters tend to be expensive,
so if you wanted a lot of different bandwidths, it may not have
been the best choice.

So you'd still see double conversion, with a good filter at the first
IF in the HF range, but as wide as the widest bandwidth you want,
and then a conversion to 455KHz or whatever where you could get more
of a range of filters. Or convert down to 50KHz, as Drake did, where
you could design good filters with relatively cheap LC circuits.

But then we also saw branch of receiver design where the first
IF would be above the signal frequency. IN the case of the shortwave
receiver, that puts it above 30MHz. That makes the image so far away
that front end tuning could really be cut down, with the real factor
being that the first mixer would see plenty of signals the receiver
isn't interested in, and could be prone to overload. Some designs
even went to a low pass filter at the front end, cutting off at
30MHz so the front end needed no tuning but saw nothing above 30MHz
where the image would be.

But once you place the IF in the 40Mhz or higher range, you've lost
the ability to build good filters. Either design limitations or cost
mean that you don't see narrow filters up there. More like 15KHz wide
or more, not really useful for shortwave listening. So there
was a move back to double conversion, with the second IF providing
the ultimate selectivity. Back to some of the tradeoffs of double
conversion, but at least image rejection was generally gone. This
wave of receivers caused other design decisions. Since the local
oscillator now had to be higher than 30MHz, stability really became
an issue, and that meant synthesized tuning took over. (Another
way of looking at it might be that you couldn't easily go to such
a high first IF unless you used synthesizer.)

And of course, conversions have also been used to add features
to a receiver, such as passband tuning.

So talking about double or triple conversion means nothing. You need
to talk about the actual IF frequency or frequencies, and the front
end selectivity, and whether the conversion is added for extra feature
or to get a basic thing.

Michael

"Caveat Lector" ) writes:
Maybe read what Elecraft sez -- URL:

http://www.elecraft.com/Apps/why_is_...ver_single.htm


Or, get a book and do it the old fashioned way.

Michael

On Sun, 13 Nov 2005 12:05:46 -0500, "Larry" wrote:

What am I missing here. Although my background is in electronics and
electrical engineering, I've specialized in power rather than communications
for thirty years. My scant and no doubt obsolete communications theory
always held that for great short-wave reception, double or even triple
conversion receivers were the norm. Now I see advertised, SW radios with
"... highly sensitive and selective latest state of the art single
conversion analog tuner circuitry....". What breakthrough has made single
conversion so state of the art?


Look up ''preselector''.

"David" wrote in message
...
On Sun, 13 Nov 2005 12:05:46 -0500, "Larry" wrote:

What am I missing here. Although my background is in electronics and
electrical engineering, I've specialized in power rather than
communications
for thirty years. My scant and no doubt obsolete communications theory
always held that for great short-wave reception, double or even triple
conversion receivers were the norm. Now I see advertised, SW radios with
"... highly sensitive and selective latest state of the art single
conversion analog tuner circuitry....". What breakthrough has made single
conversion so state of the art?


Look up ''preselector''.


Oh Gee -- A tuned RF Amplifier
What a novel approach (;-)

My Hallicrafters S-40B circa 1948 had one of these
--
CL -- I doubt, therefore I might be !

"Michael Black" wrote in message
...

"Larry" ) writes:
What am I missing here. Although my background is in electronics and
electrical engineering, I've specialized in power rather than
communications
for thirty years. My scant and no doubt obsolete communications theory
always held that for great short-wave reception, double or even triple
conversion receivers were the norm. Now I see advertised, SW radios with
"... highly sensitive and selective latest state of the art single
conversion analog tuner circuitry....". What breakthrough has made single
conversion so state of the art?


The number of conversions in a receiver means nothing. It's the detail
behind it that counts.

When Howard Armstrong came up with the superheterodyne receiver during or
right after WWI, tubes were pretty non-existent in terms of specs. You
needed
to convert radio to a lower frequency to get any sort of amplification.
So
all superhets in the early days went to a lower frequency.

But then they realized a problem with that. Every time two frequencies
are heterodyned together, the sum and the difference result. This means
that there is an image frequency, ie one that is incidental to the
heterodyning but which you you don't want. If your IF frequency is
455KHz, and you want to receive WWV at 10MHz, there will also be an
image twice the IF frequency away (higher or lower depending on
whether the receiver's local oscillator is higher or lower than the
signal frequency).

To get rid of that image frequency, you need the front end to be
selective enough to knock it out. At low frequencies, like the AM
broadcast band, it's easy, because the image is distant from the
desired signal by a fair amount. But as you move into the shortwave
frequencies, that 455KHz becomes a smaller and smaller percentage of the
signal frequency, and it becomes harder to get rid of the image. There
were all kinds of cheap receivers in the past (and maybe even today) that
had 455KHz IFs and you'd see reviews and they'd say "basically there is
no image rejection on the 20 to 30MHz band. The only way to stay with
455KHz and get good image rejection is to add more tuned circuits at
the front end, which some receivers like the HRO, did.

You can raise the IF frequency to improve image rejection. If you've
got a 9MHz IF, then you can get by with fairly little front end
selectivity,
because the image is 18MHz away from the signal you want to tune. It's
easy to reject a signal that far off.

But for quite some time, this wasn't possible because nobody could make
filters that high up. So the double-conversion receiver came into use.
Convert the signal down to a not too low frequency, to improve image
rejection, but then convert down to the usual 455KHz after that to get
good selectivity. If you have enough selectivity at the first IF so
it can reject a signal 910KHz away (and this is relatively easy for a
fixed
IF where you don't have to tune a bunch of tuned circuits at the same
time across the band), then you've mostly solved the image rejection
problem.

The double conversion in this case is just a workaround, to get good
image rejection, but also good selectivity with the second IF frequency.

When double conversion first hit, they'd often do a mix, where the
receiver would be single conversion to 455KHz on the lower bands, and
then a stage of selectivity at 2 or 3MHz would kick in on the higher
band(s) where it was needed, before another conversion to 455KHz.
These still used a tuneable local oscillator on the first mixer.

Of course, one whole layout of double conversion was to make the
first local oscillator crystal controlled. Then you'd have what
amounted to a tuneable receiver with a 455KHz IF, that tuned a fixed
range, often 500KHz. It would tune something like 3 to 3.5MHz, and
the first conversion would convert the desired signals to that range.
One disadvantage of this is that you needed a crystal for every 500KHz
or whatever the tuneable portion tuned. (Sometimes it got far worse,
with the receiver tuning 200KHz at a time.) On the other hand, the
advantage of this scheme was that by having the receiver tune a small
segment of the spectrum, and only tune that 3 to 3.5MHz band, you could
afford to make it linear tuning, and could afford to calibrate it well.
So these receivers brought in a level of tuning accuracy that often
hadn't been seen before.

There is another problem with conversion besides images. Every conversion
decreases the immunity to overload, adds complication, and adds another
oscillator that if not carefully shielded and layed out, will cause
spurious responses.

So starting in the late fifties and early sixties, a new wave of
single conversion receivers hit. Crystal filters came along, that
offered good selectivity in the HF range, 9MHz being a common frequency.
That gave good selectivity and allowed for good image rejection with
only one IF frequency. Instead of having the ultimate selectivity way
down the signal chain, you could place it right after the first mixer,
leaving a stage or two before that good crystal filter. (Since the stages
after the crystal filter only had to see what was within the bandwidth
of that filter, it took a really strong signal to overload anything after
that filter, while in some of the previous examples many stages would
be seeing a lot of signal.)

Of course there were problems with that scheme. If the IF is in the
spectrum you want to receive, it can't be used around that frequency.
So there'd be a small gap around the IF frequency that you couldn't
really use the receiver. Also, crystal filters tend to be expensive,
so if you wanted a lot of different bandwidths, it may not have
been the best choice.

So you'd still see double conversion, with a good filter at the first
IF in the HF range, but as wide as the widest bandwidth you want,
and then a conversion to 455KHz or whatever where you could get more
of a range of filters. Or convert down to 50KHz, as Drake did, where
you could design good filters with relatively cheap LC circuits.

But then we also saw branch of receiver design where the first
IF would be above the signal frequency. IN the case of the shortwave
receiver, that puts it above 30MHz. That makes the image so far away
that front end tuning could really be cut down, with the real factor
being that the first mixer would see plenty of signals the receiver
isn't interested in, and could be prone to overload. Some designs
even went to a low pass filter at the front end, cutting off at
30MHz so the front end needed no tuning but saw nothing above 30MHz
where the image would be.

But once you place the IF in the 40Mhz or higher range, you've lost
the ability to build good filters. Either design limitations or cost
mean that you don't see narrow filters up there. More like 15KHz wide
or more, not really useful for shortwave listening. So there
was a move back to double conversion, with the second IF providing
the ultimate selectivity. Back to some of the tradeoffs of double
conversion, but at least image rejection was generally gone. This
wave of receivers caused other design decisions. Since the local
oscillator now had to be higher than 30MHz, stability really became
an issue, and that meant synthesized tuning took over. (Another
way of looking at it might be that you couldn't easily go to such
a high first IF unless you used synthesizer.)

And of course, conversions have also been used to add features
to a receiver, such as passband tuning.

So talking about double or triple conversion means nothing. You need
to talk about the actual IF frequency or frequencies, and the front
end selectivity, and whether the conversion is added for extra feature
or to get a basic thing.

Michael

Nice post. Quite informative.

--
rb

"Ron Baker, Pluralitas!" wrote in message
...

"Michael Black" wrote in message
...

"Larry" ) writes:
What am I missing here. Although my background is in electronics and
electrical engineering, I've specialized in power rather than
communications
for thirty years. My scant and no doubt obsolete communications theory
always held that for great short-wave reception, double or even triple
conversion receivers were the norm. Now I see advertised, SW radios with
"... highly sensitive and selective latest state of the art single
conversion analog tuner circuitry....". What breakthrough has made
single
conversion so state of the art?


The number of conversions in a receiver means nothing. It's the detail
behind it that counts.

When Howard Armstrong came up with the superheterodyne receiver during or
right after WWI, tubes were pretty non-existent in terms of specs. You
needed
to convert radio to a lower frequency to get any sort of amplification.
So
all superhets in the early days went to a lower frequency.

But then they realized a problem with that. Every time two frequencies
are heterodyned together, the sum and the difference result. This means
that there is an image frequency, ie one that is incidental to the
heterodyning but which you you don't want. If your IF frequency is
455KHz, and you want to receive WWV at 10MHz, there will also be an
image twice the IF frequency away (higher or lower depending on
whether the receiver's local oscillator is higher or lower than the
signal frequency).

To get rid of that image frequency, you need the front end to be
selective enough to knock it out. At low frequencies, like the AM
broadcast band, it's easy, because the image is distant from the
desired signal by a fair amount. But as you move into the shortwave
frequencies, that 455KHz becomes a smaller and smaller percentage of the
signal frequency, and it becomes harder to get rid of the image. There
were all kinds of cheap receivers in the past (and maybe even today) that
had 455KHz IFs and you'd see reviews and they'd say "basically there is
no image rejection on the 20 to 30MHz band. The only way to stay with
455KHz and get good image rejection is to add more tuned circuits at
the front end, which some receivers like the HRO, did.

You can raise the IF frequency to improve image rejection. If you've
got a 9MHz IF, then you can get by with fairly little front end
selectivity,
because the image is 18MHz away from the signal you want to tune. It's
easy to reject a signal that far off.

But for quite some time, this wasn't possible because nobody could make
filters that high up. So the double-conversion receiver came into use.
Convert the signal down to a not too low frequency, to improve image
rejection, but then convert down to the usual 455KHz after that to get
good selectivity. If you have enough selectivity at the first IF so
it can reject a signal 910KHz away (and this is relatively easy for a
fixed
IF where you don't have to tune a bunch of tuned circuits at the same
time across the band), then you've mostly solved the image rejection
problem.

The double conversion in this case is just a workaround, to get good
image rejection, but also good selectivity with the second IF frequency.

When double conversion first hit, they'd often do a mix, where the
receiver would be single conversion to 455KHz on the lower bands, and
then a stage of selectivity at 2 or 3MHz would kick in on the higher
band(s) where it was needed, before another conversion to 455KHz.
These still used a tuneable local oscillator on the first mixer.

Of course, one whole layout of double conversion was to make the
first local oscillator crystal controlled. Then you'd have what
amounted to a tuneable receiver with a 455KHz IF, that tuned a fixed
range, often 500KHz. It would tune something like 3 to 3.5MHz, and
the first conversion would convert the desired signals to that range.
One disadvantage of this is that you needed a crystal for every 500KHz
or whatever the tuneable portion tuned. (Sometimes it got far worse,
with the receiver tuning 200KHz at a time.) On the other hand, the
advantage of this scheme was that by having the receiver tune a small
segment of the spectrum, and only tune that 3 to 3.5MHz band, you could
afford to make it linear tuning, and could afford to calibrate it well.
So these receivers brought in a level of tuning accuracy that often
hadn't been seen before.

There is another problem with conversion besides images. Every
conversion
decreases the immunity to overload, adds complication, and adds another
oscillator that if not carefully shielded and layed out, will cause
spurious responses.

So starting in the late fifties and early sixties, a new wave of
single conversion receivers hit. Crystal filters came along, that
offered good selectivity in the HF range, 9MHz being a common frequency.
That gave good selectivity and allowed for good image rejection with
only one IF frequency. Instead of having the ultimate selectivity way
down the signal chain, you could place it right after the first mixer,
leaving a stage or two before that good crystal filter. (Since the stages
after the crystal filter only had to see what was within the bandwidth
of that filter, it took a really strong signal to overload anything after
that filter, while in some of the previous examples many stages would
be seeing a lot of signal.)

Of course there were problems with that scheme. If the IF is in the
spectrum you want to receive, it can't be used around that frequency.
So there'd be a small gap around the IF frequency that you couldn't
really use the receiver. Also, crystal filters tend to be expensive,
so if you wanted a lot of different bandwidths, it may not have
been the best choice.

So you'd still see double conversion, with a good filter at the first
IF in the HF range, but as wide as the widest bandwidth you want,
and then a conversion to 455KHz or whatever where you could get more
of a range of filters. Or convert down to 50KHz, as Drake did, where
you could design good filters with relatively cheap LC circuits.

But then we also saw branch of receiver design where the first
IF would be above the signal frequency. IN the case of the shortwave
receiver, that puts it above 30MHz. That makes the image so far away
that front end tuning could really be cut down, with the real factor
being that the first mixer would see plenty of signals the receiver
isn't interested in, and could be prone to overload. Some designs
even went to a low pass filter at the front end, cutting off at
30MHz so the front end needed no tuning but saw nothing above 30MHz
where the image would be.

But once you place the IF in the 40Mhz or higher range, you've lost
the ability to build good filters. Either design limitations or cost
mean that you don't see narrow filters up there. More like 15KHz wide
or more, not really useful for shortwave listening. So there
was a move back to double conversion, with the second IF providing
the ultimate selectivity. Back to some of the tradeoffs of double
conversion, but at least image rejection was generally gone. This
wave of receivers caused other design decisions. Since the local
oscillator now had to be higher than 30MHz, stability really became
an issue, and that meant synthesized tuning took over. (Another
way of looking at it might be that you couldn't easily go to such
a high first IF unless you used synthesizer.)

And of course, conversions have also been used to add features
to a receiver, such as passband tuning.

So talking about double or triple conversion means nothing. You need
to talk about the actual IF frequency or frequencies, and the front
end selectivity, and whether the conversion is added for extra feature
or to get a basic thing.

Michael

Nice post. Quite informative.

--
rb


DITTO--
CL -- I doubt, therefore I might be !

On Sun, 13 Nov 2005 12:05:46 -0500, Larry wrote:

What am I missing here. Although my background is in electronics and
electrical engineering, I've specialized in power rather than communications
for thirty years. My scant and no doubt obsolete communications theory
always held that for great short-wave reception, double or even triple
conversion receivers were the norm. Now I see advertised, SW radios with
"... highly sensitive and selective latest state of the art single
conversion analog tuner circuitry....". What breakthrough has made single
conversion so state of the art?

DSP -


--
Korbin Dallas
The name was changed to protect the guilty.

Michael Black - Thank Your Very Much ! )
It Was Worth Re-Posting ~ RHF

ABOUT - Radios : The Number of Conversions in a Receiver means
nothing...
http://groups.yahoo.com/group/Shortw...a/message/6514

" The Number of Conversions in a Receiver Means Nothing.
.. . . It's the Detail Behind It that Counts. "
- by Michael Black

* * * EXTRACTED from NewsGroups : Rec.Radio.Shortwave
= = = From: * (Michael Black)
= = = Date: 13 Nov 2005 17:50:05 GMT
= = = Local: Sun, Nov 13 2005 9:50 am
= = = Subject: A "Single Conversion" Question


iane ~ RHF
.
.
Tous Sont Bienvenus ! - - - Groupe par Radio
d'auditeur d'onde courte pour des Antennes de SWL
http://groups.yahoo.com/group/Shortwave-SWL-Antenna/
.
Alle Sind Willkommen ! - - - Shortwave Radiozuhörer
Gruppe für SWL Antennen
http://groups.yahoo.com/group/Shortwave-SWL-Antenna/
.
Tutti Sono Benvenuti ! - - - Gruppo Radiofonico
dell'ascoltatore di onda corta per le Antenne di SWL
http://groups.yahoo.com/group/Shortwave-SWL-Antenna/
.
Todos São Bem-vindos ! - - - Grupo de Rádio
do ouvinte do Shortwave para Antenas de SWL
http://groups.yahoo.com/group/Shortwave-SWL-Antenna/
.
Ð’Ñ�е Ð*адушны ! - - - Группа оператора
на приеме коротковолнового диапазона
Radio дл� Aнтенн SWL
http://groups.yahoo.com/group/Shortwave-SWL-Antenna/
.
¡Todos Son Agradables! - - - Grupo de Radio del oyente
de la onda corta para las Antenas de SWL
http://groups.yahoo.com/group/Shortwave-SWL-Antenna/
.
= = = = = Translation = = = = =
All are Welcome - - - To Join the Shortwave Listeners
(SWL) Antenna Group on YAHOO !
http://groups.yahoo.com/group/Shortwave-SWL-Antenna/
.
.
.. .